Air cooled magnetic clutch and brake

ABSTRACT

A magnetic friction clutch wherein two disk-shaped armatures are movable axially of and rotate with the driven shaft. One of the armatures is adjacent to a flywheel which is rotated by the output shaft of an electric motor and the other armature is adjacent to a stationary or rotary braking member. Each armature has a ring-shaped nave which is mounted on the driven shaft and a ring-shaped rim which surrounds and is magnetically separated from the respective rim. Annular facings of magnetically nonconductive material are provided on each of the armatures between the respective nave and rim and their exposed surfaces are flush with pole faces provided on the corresponding rim and nave. Two windings are mounted in the space between the two armatures and one thereof is energizable to cause the facing and the pole faces of one armature to bear against the flywheel, the other winding being energizable to cause the facing and the pole faces of the armature to bear against the braking member. Channels in the braking member, naves of the armatures and the flywheel serve to convey streams of cooling air which are induced by annuli of blades on the flywheel. The material of those portions of each rim and nave which are adjacent to the respective pole faces exhibits the same resistance to wear as the material of the facings.

United States Patent [191 Marti Dec. 11, 1973 AIR COOLED MAGNETIC CLUTCHAND BRAKE V [75] Inventor: Willi Hermann Marti, Basel, Switzerland [73]Assignee: Delmoran AG, Basel, Switzerland [22] Filed: Dec. 3, 1971 [21]Appl. No.1 204,635

[30] Foreign Application Priority Date 3,368,657 2/1968 Wrensch et al.192/18 B Primary Examiner-Benjamin W. Wyche Attorney-Michael S. Striker[57] ABSTRACT v A magnetic friction clutch wherein two disk-shapedarmatures are movable axially of and rotate with the driven shaft. Oneof the armatures is adjacent to a flywheel which is rotated by theoutput shaft of an electric motor and the other armature is adjacent toa stationary or rotary braking member. Each armature has a ring-shapednave which is mounted on the driven shaft and a ring shaped rim whichsurrounds and is magnetically separated from the respective rim. Annularfacings of magnetically non-conductive material are provided on each ofthe armatures between the respective nave and rim and their exposedsurfaces are flush with pole faces provided on the corresponding rim andnave. Two windings are mounted in the space between the two armaturesand one thereof is energizable to cause the facing and the pole faces ofone armature to bear against the flywheel, the other winding beingenergizable to cause the facing and the pole faces of the armature tobear against the braking member. Channels in the braking member, navesof the armatures and the flywheel serve to convey streams of cooling airwhich are induced by annuli of blades on the flywheel. The material ofthose portions of each rim and nave which are adjacent to the respectivepole faces exhibits the same resistance to wear as the material of thefacings.

22 Claims, 2 Drawing Figures PATENIEDMc 1 1 I973 SHEET 1 OF 2 2 RN 9W2 mAIR COOLED MAGNETIC CLUTCH AND BRAKE BACKGROUND OF THE INVENTION Thepresent invention relates to magnetic clutches in general, and moreparticularly to improvements in magnetic clutches of the type wherein adriving shaft which receives torque from a motor carries a flywheel andcan be coupled to or uncoupled from a driven shaft in response tochanges in the condition of energization of winding. Still moreparticularly, the invention relates to improvements in clutches of thetype wherein two disk-shaped armatures are disposed between a flywheeland a stationary or rotary braking member and are mounted on the drivenshaft to rotate the driven shaft at the speed of the flywheel inresponse to energization of a first winding which causes one of thearmatures to bear against the flywheel and to either decelerate orarrest the driven shaft in response to energization of a second windingwhich causes the other armature to bear against the braking member.

German printed publication No. 1,265,843 discloses a magnetic clutchwherein the driven shaft carries two fixedly mounted elastic washers forring-shaped armatures which are disposed between a constantly drivenflywheel of the motor and a braking member. The armature surround therespective washers and one thereof is caused to engage the flywheel inresponse to energization of a first winding with attendant deformationof the respective elastic washer; the other armature bears against thebraking member in response to energization of a second winding whichresults in deformation of the other washer. The flywheel and the brakingmember carry ring-shaped magnets which can be engaged by ring-shapedfriction generating facings which are disposed radially inwardly of therespective armatures. The magnetic forces which cause the facingsrespectively to bear against the flywheel and the braking member areactive only in the regions surrounding the respective facings and thearea of contact between the braking member or the flywheel on the onehand and the respective facing on the other hand is relatively small.Therefore, the electromagnets including the windings and the associatedarmatures must generate substantial forces, especially if the drivenshaft is to be rapidly accelerated by the flywheel or rapidlydecelerated by the braking member. The power requirements of theelectromagnets are further increased due to the fact that the armaturesare mounted on elastic washers which must be deformed before therespective facings can be moved into requisite friction generatingengagement with adjoining magnets. The efficiency of a clutch isnormally defined as the ratio between the transmitted output and therequired ampere turn member; such efficiency is very low in the clutchesof the just outlined character. Moreover, due to the high number ofampere turns, the magnetic inertia of the clutches is very high so thatthe switching time (namely, the interval which elapses between theenergization of a winding and the desired acceleration or decelerationof the driven shaft) is too long. still further, the friction heat isgenerated mainly in a region which is disposed radially inwardly of thearmatures (because the facings are surrounded by the armatures) and,therefore, such heat cannot be dissipated with a desired degree ofefficiency, especially if the windings are to be energized at frequentintervals.

US. Pat. No. 3,254,746 discloses a clutch for electric motors whichdispenses with the aforediscussed elastic washers. Instead the twoarmatures are movable axially of but rotate with the driven shaft. Botharmatures are confined in a cup-shaped end bell whose open side facesthe flywheel on the driving shaft. The armatures are surrounded by therespective windings so that their diameters, and hence the diameters ofthe facings (one of which serves to engage the flywheel and the other ofwhich serves to engage the breaking number), are small. Therefore, theefficiency of such clutch is low, their switching-times are long and thedissipation of friction heat presents serious problems. Furthermore, theaxial length of the clutch is considerable so that the clutch cannot beused in apparatus wherein the motor which drives the flywheel is closelyadjacent to the part or parts which receive torque from the drivenshaft. The paths for the magnetic flux are very long and the magneticforces act only upon the radially outwardly located portions of thefacings. Therefore, the armature must be stable and hence heavy andbulky in order to insure at least nearly uniform pressure between thefacings and the respective magnets on the flywheel and braking member.

SUMMARY OF THE INVENTION An object of the invention is to provide anovel and improved magnetic friction clutch with two diskshapedarmatures (hereinafter called disks for short) wherein the entiresurface of each facing can be brought into uniform friction generatingengagement with the adjacent magnet of a rotary or stationary part, suchas a flywheel and a stationary or rotary braking member.

Another object of the invention is to provide novel and improved disksfor use in a magnetic friction clutch, particularly in a magnetic clutchwith two disks which are movable axially of and rotate with the drivenshaft.

A further object of the invention is to provide a magnetic frictionclutch with novel and improved means for dissipating or leading awayheat which is generated in response to energization of one or morewindings as well as of such heat which is generated as a result offrictional engagement between a facing and the adjacent rotarystationary part.

An additional object of the invention is to provide a magnetic frictionclutch wherein the friction generating areas of the disks are muchlarger than in presently known clutches without necessitating anoverdimensioning of the disks.

Still another object of the invention is to provide a clutch which canfurnish extremely short switching times, which can transmit substantialtorque with minimal delays, and which occupies less room than presentlyknown clutches with identical torque-transmitting and brakingcharacteristics A further object of the invention is to provide a clutchwherein the wear on the facings is only a small fraction of the wear onthe facings of conventional clutches and wherein the width of air gapsbetween the disks and the adjoining parts remains unchanged even afterextremely long periods of use.

The invention is embodied in a structure which comprises coaxial drivingand driven shafts whereby the driving shaft constitutes the outputelements of an electric or other motor and the driven shaft constitutesthe input element of a machine or the like which receives torque fromthe motor at desired intervals, a flywheel secured to and arranged torotate with the driving shaft, a fixed or rotary braking member axiallyspaced from the flywheel, first and second disks disposed between theflywheel and the braking member and being movable axially of but alwaysrotating with the driven shaft, and first and second windings which arerespectively energizable to urge annular facings provided on the firstand second disks against the flywheel and the braking member so that thedriven shaft is rotated at the speed of the driving shaft in response toenergization of the first winding and the driven shaft is arrested orrotates at the lesser speed of the braking member in response toenergization of the second winding.

In accordance with a feature of the invention, each disk comprisesmagnetically conductive inner and outer ring-shaped portions which arecoaxial with each other and with the driven shaft and are magneticallyinsulated from each other by plate-like annuli or by one or more slotsprovided in the disks between their inner and outer portions. Thefacings are rings which are mounted on the respective disks-between theinner and outer ring-shaped portions and have exposed surfaces which areflush with poles faces provided on the corresponding inner and outerring-shaped portions.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved clutch itself, however, both as to its construction and itsmode of operation, together with additional features and advantagesthereof, will be best understood upon perusal of the following detaileddescription of certain specific embodiments with reference to theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an axial sectional view of amagnetic clutch which embodies one form of the invention; and

FIG. 2 is an axial sectional view of a modified magnetic clutch.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1,there is shown a portion of an electric motor having an output shaft ordriving shaft 1 which is assumed to rotate at a constant speed, e.g., at3,000 RPM. The output shaft 1 is connected with and rotates a flywheel 2having a ring-shaped body 3 the right-hand end face of which carries aring 4 of magnetically conductive material. That end face of the ring 4which is turned away from the ring-shaped body 3 (i.e., in a directionto the right, as viewed in FIG. 1) has a radially outermost portionprovided with an annulus of fan blades or vanes 5. Additional fan bladesor vanes 7 are provided on the left-hand end face of the body 3. Theflywheel 2 is further provided with an annulus of axially parallelventilating channels or openings 8. r

The housing of the clutch includes an annular portion in the form ofacupped bearing member 11 which has a hub or sleeve 9 for two axiallyspaced antifriction bearings 10. The inner races of these bearingssurround a driven shaft 12 which is coaxial with the output shaft 1 ofthe motor. The right-hand end portion of the driven shaft 12 can beconnected with a pulley (not shown) which can rotate the main shaft of asewing machine by means of one or more V-belts. It is clear, however,that the sewing machine constitutes but one of a host of machines orapparatus whose main or working shafts can receive torque by way of theimproved clutch.

The left-hand end portion of the driven shaft 12 carries two axiallymovable disk-shaped armatures, namely, a braking disk 15 and a clutchdisk 14. These disks share all angular movements of the driven shaft 12.To this end, the left-hand end portion of the driven shaft 12 is rigidlyconnected with a sleeve 16 the external surface of which is providedwith axially parallel splines or with involute teeth mating withcomplementary splines or teeth of the disks 14 and 15. Suchcomplementary splines or teeth are provided in two ringshaped innerportions or naves 17, 18 of the disks I4, 15. The sleeve 16 consists ofa material of low magnetic conductivity, such as a suitable syntheticplastic-substance.

The nave 17 of the disk 14 is concentric with and is spacedly surroundedby an outer ring-shaped portion or rim 19 which is connected with thenave 17 by means of a plate-like annulus 20 consisting of aluminum,another light metal or a synthetic plastic substance.

The nave 18 of the disk 15 is concentric with and is spacedly surroundedby an outer ring-shaped portion or rim 21 which is connected with thenave 18 by means of a plate-like annulus 22 consisting of a light metalor a synthetic plastic substance. The plates 20, 22 are provided withring-shaped recesses for ring-shaped friction generating facings 23, 24.The exposed surface of the facing 23 is flush with the left-hand endfaces of the nave 17 and rim 19, and the exposed surface of the facings24 is flush with the right-hand end faces of the nave 18 and rim 21. Thefacing 23 is adjacent to the ring 4 of the flywheel 2 and the facing 24is adjacent to the magnetically conductive braking ring 32 of a brakingmember 25 in the bearing member 11.

The portions 17, 19 and 18, 21 of the disks 14, 15 consist of amagnetically conductive material whose resistance to wear preferablyclosely approximates or equals that of the facings 23, 24. This insuresthat, when the disk 14 is caused to engage the flywheel 2, the wear onthe facing 23 is the same as the wear on the nave 17 and rim 19, as wellas that the wear on the facing 24 equals the wear on the nave 18 and rim21 when the disk 15 is caused to engage the braking member 25. It wasfound that sintered iron permeated with polytetrafluorethylene isparticularly suited for the manufacture of disk portions 17, 18, 19 and21, and that sintered bronze, also permeated withpolytetrafluorethylene, is particularly suited for the manufacture offacings 23 and 24. The naves 17, 18 are respectively provided withaxially parallelventilating channels or openings 26, 27.

The braking member 25 comprises an annular body portion 30 which isprovided with projections or ribs 31 extending axially toward the disk15. The body portion 30 is connected with the magnetically conductivebraking ring 32 which can be bolted or screwed to the body portion 30and has a flat left-hand end face adjacent to the ring 15. Radialcooling channels 33 are defined by the projections 31 between the bodyportion 30 and the ring 32. The braking member 25 is connected with aworm wheel 34 is rotatably mounted on the sleeve 9 of the bearing member11. The worm wheel 34 receives torque from a auxiliary motor (not shown)and rotates at a speed which is less than the speed of the outputshaft 1. Drive means of the just outlined character are known in theart, for example, from German Patent No. 1,159,745. The rings 4 and 32preferably consistof hardened steel and are provided with flat end faceswhich respectively face the disks 14 and 15'.

The annular space between the plates 20, 22,.rims 19, 21 and naves 17,18 accommodates a stationary frame for two ring-shaped windings 42, 43.The frame has a substantially l-shaped cross-sectional outline andcomprises two profiled sheet metal rings 36,37 whose inner flanges arerespectively adjacent to have naves 17, 18, whose outer flanges arerespectively adjacent to i the rims 19, 21 and whose webs are adjacentto each other. The webs of the profiled rings 36, 37 are welded orotherwise secured to the opposite sides of .a ringshaped. plate-likecarrier :38-whichis secured to an annular intermediate portion 41 oftheclutch housing. The annular portion 41 is disposed betweenthe bearingmember 11 and an annular housing portion 40 surrounding the motor whichincludes the output shaft 1. As shown in FIG. 1, the carrier 38islocated in a plane which is normal to the common axis of theshafts 1, 12and with respect to which the disks 14,,15are at least substantiallymirror symmetrical. to each other. The windings 42, 43 are respectivelymounted in the profiled rings 36, 37.

The entire internal surfaces of the inner flanges .of profiled rings 36,37 are respectively adjacent to but slightly spaced from the externalsurfaces of the naves 17, 18. The rims 19, 21 are slightly spaced fromthe external surfaces of the outer flanges of profiled rings 36, 37 andeach of these rims overlaps a substantial portion of the respectiveexternal surface, i.e., though the rims 19, 21 do not extend all the wayto the carrier 38, they still define with the outer flanges of the rings36, 37 an annular air gap of considerable axial length. The thickness ofthe rims 19, 21 is selected in such a way that the width of air gapsbetween these rims and the outer flanges of the profiled rings 36,37equals or closely approximates the width of air gaps between the innerflanges of the rings, 36, 37 and the external surfaces of the naves 17,18. Axially parallel cooling channels 45 extend between the rims 19, 21.and the annular housing portion 41; such channels communicate with eachother by way of cutouts or windows (not shown) in the carrier 38. Theright-hand channels 45 further communicate with air-admitting inletopenings 46 in the bearing member 11 and the left hand channels 45further communicate with air-evacuating outlet openings 47in the annularhousing portion 41.-

The provision of air gaps having a substantial length, as considered inthe axial direction of the disks l4 and 15, is desirable because suchgaps reduce the magnetic resistance and scattering so that the clutchcan operate properly with a relatively small number of ampere turns. Themounting of the frame 3638 for the windings 42, 43 in the annular spacebetween the disks 14, 15 is desirable because the frame occupies littleroom, because the frame occupies room which is available in the housingof the clutch, and also because such mounting of the windings 42, 43ii1sures short paths for the magnetic lines of force.

The operation If the winding 42 in the left-hand profiled ring 36 isenergized in a manner not forming part of the present invention, theredevelops a magnetic flux which surrounds the winding 42 and is indicatedby the broken line 48. Such flux passes radially through the ring 36,across the axially parallel air gap between the inner flange of the ring36 and the nave 17, axially through the nave 17, across the radiallyextending gap between the left-hand end face or pole face of the nave 17and the magnetically conductive ring 4, radially through the ring 4,across the radially extending gap between the ring 4 and the left-handend face or pole face of the rim 19, axially through the rim 19, andback into the ring 36across the axially parallel air gap between the rim19 and the outer flange of the ring 36. Consequently, the disk 14 isforced against the flywheel 2, i. e., the pole faces of the nave 17 andrim 19 as well as the exposed surface of the facing 23 are caused tobear against the smooth right-hand end face of the ring 4. Thus, thedisk 14 couples the flywheel 2 (and hence the output shaft 1) with thedriven shaft "12 which then rotates at the speed of the shaft 1. Theplate 20 prevents a magnetic short-circuiting of the disk 14, i. e., adirect passage of magnetic flux from the nave 17 to the rim 19 of thedisk 14 without passing radially through the ring 4.

The magnetic forces which transmit torque from the output shaft 1 to thedriven shaft 12 are effective radially inwardly as well as radiallyoutwardly of the facing 23. This will be readily understood upon perusalof the preceding description of the magnetic flux (line 48) whichdevelops when thewinding 42 is energized. Such distribution of magneticforces in response to energization of the winding 42 insures that allportions of the facing 23 are passed against the ring 4 with the sameforce, even if the mechanical stability (and hence the weight andinertia) of the disk 14 is low. This is desirable because a uniformdistribution of forces insures equal wear on all portions of the disk 14which engage the ring 4.

The low weight (and hence the low average or median inertia radius) ofthe disk 14 is further attributable to the fact that the plate 20 whichconnects the nave 17 with the rim 19 consists of light metal or alightweight synthetic plastic material. The combined area of frictiongenerating surfaces (on the ring 4 and portions 17, 19 of the disk 14)is very large which is desirable in 'order to insure the transmission ofsubstantial torque when the winding 42 is energized. The provision ofsuch large friction generating surfaces is due to the fact that theexposed surface of the facing 23 is flush with the pole faces of thenave 17 and rim 19 and also because the wear on the facing 23 is atleast substantially identical with the wear on the disk portions 17, 19.Consequently, the combined area of friction generating surfaces on theparts 17, 23, 19 remains unchanged even after extensive use of theclutch. The paths for the magnetic flux are very short and such pathsare substantially symmetrical to the median radius of the facing 23. Dueto the fact that the pole faces of the disk portions 17, 19 are flushwith the exposed surface of the facing 23, and also because each of theparts 17, 23, 19 consists of a metallic carrier for a synthetic plasticlubricant, the width of the axially parallel air gaps between theflanges of the profiled ring 36 and the portions 17, 19 of the disk 14can be maintained at an extremely low value which is highly desirable inmany types of magnetic friction clutches, i.e., in all those clutcheswherein the magnetic resistance of the paths for magnetic flux should beheld to a minimum. Consequently, relatively small magnetic forcessuffice to insure the transmission of substantial torque with extremelyshort switching times (i.e., the length of intervals which elapsebetween energization of the winding 42 and the rotation of driven shaft12 at the exact speed of the output shaft 1).

The situation is analogous when the winding 43 is energized to cause theexposed surface of the facing 24 and the pole faces of the nave 18 andrim 2] to bear against the smooth left-hand end face of the magneticallyconductive ring 32 which forms part of the braking member 25. Themagnetic flux which develops on energization of the winding 43 isindicated by the broken line 49.

The width of the radial air gap between the ring 4 andv the disk 14 canbe varied by removal or insertion of one or more suitable shims oranalogous inserts 50 between the adjacent radially extending surfaces ofthe housing portions 40 and 41. The width of the radial airgap betweenthe ring 32 and the disk 15 can be changed by inserting or removing oneor more shims or analogous inserts (not shown) between the annularhousing portions 11 and 41.

The heat which develops in the winding 42 or 43, as well as the heatwhich develops when the disk 14 or 15 is respectively caused to engagethe ring 4 or 32 (so that the driven shaft 12 respectively rotates atthe speed of the output shaft 1 or the worm wheel 34) can be readily ledaway by streams of air which are circulated in response to rotation ofthe flywheel 2, i.e., when the motor including the shaft 1 is on. Suchair streams are caused to flow around at least one side but preferablyalong opposite sides of each such part which is particularly affected byheat. Thus, a first cooling air stream 52 is induced by the blades 7 ofthe continuously rotating flywheel 2 and is caused to flow from theinlet opening 46 of the bearing member 11 into the radial channels 33 ofthe braking member 25. Such air stream is drawn through the ventilatingchannels 27, 26 of the naves 18, 17 and through the channels 8 of theflywheel 2 to flow along the left-hand side of the flywheel through oneor more outlet openings of the housing portion 40. A second cooling airstream 53 is induced by the blades of the ring 4 to flow from the inletopenings 46 through the channels 45 to leave the magnetic clutch by wayof the outlet openings 47 in the annular housing portion 41.

The facings 23, 24 could be made of cork impregnated with oil or greasein a manner known from the art. However, the aforedescribed facings arepreferred because their resistance to volumetric changes in response tochanges in temperature, their resistance to wear, and their resistanceto permanent deformation in response to sudden mechanical stresses aremuch more satisfactory than the resistance of cork facings. Thus, byutilizing sintered bronze or another sintered metal which ismagnetically non-conductive and which is impregnated withpolytetrafluorethylene or another suitable synthetic plastic lubricant,the width of the gaps between the facings 23, 24 and the adjacentsurfaces of the rings 4, 32 can be reduced to a small fraction of thewidth which is necessary if the facings consist of cork. The combinedarea of the exposed surfaces of facings 23, 24 and the pole faces of therespective naves and rims 17, 19 and 18, 21 is very large so that eventhough the disks 14, are of lightweight construction, they can insurepractically instantaneous acceleration or deceleration of the drivenshaft 12, depending upon whether the energized winding 42 causes thedisk 14 to bear against the ring 4 of the flywheel 2 or the energizedwinding 43 causes the disk 15 to bear against the ring 32 of tne brakingmember 25. Since the wear of the material of the naves 17, 18 and rims19, 21 (or at least of those parts of such rims and naves which areadjacent to the respective pole faces) is preferably identical withthewear on the facings 23, 24, the area of the exposed surfaces offacings 23, 24 plus the area of pole faces of the disk portions 17, 19and 18, 21 remains practically unchanged, even after extended periods ofuse of the clutch.

' Proper cooling of the flywheel 2, disks 14,15 and braking member 25 isof particular importance when the clutch of FIG. 1 is engaged ordisengaged at frequent intervals, for example, when the clutch isinterposed between an electric motor and an industrial sewing machine.The aforedescribed cooling channels have been found to be highlyeffective to insure rapid withdrawal of heat which develops as a resultof friction between the disks 14, 15 and the parts 2, 25 as well as suchheat which develops in response to energization of the windings 42, 43.The cooling air stream 53 which is induced by the blades 5 at theright-hand side of the flywheel 2 cools the radially outermost 'parts ofthe disks 14, 15 by flowing along the rims 19, 21, whereas the airstream 52 which is induced by the blades 7 and the left-hand side of theflywheel 2 cools the braking member 25, the inner portions of disks 15,14 and the flywheel 2.

The clutch of FIG. 2 comprises a modified coupling disk 66 and amodified braking disk 67. The output shaft or driving shaft 1 of theelectric motor drives a flywheel 56 having a ring-shaped body 57 therighthand end face of which is provided with vanes or blades. Amagnetically conductive ring 59 is secured to the body 57 in such a waythat the parts 57, 59 define radially extending ventilating channels 60.The ring 59 can be screwed or bolted to the body 57.

An annular bearing member 62 which constitutes a portion of the clutchhousing accommodates two of three antifriction bearings 63, 64, 65 forthe driven shaft 12. The bearing 65 is mounted in the hub of theflywheel 56. The left-hand end portion of the driven shaft 12 is rigidlyconnected with an externally splined plastic sleeve 16 which rotateswith but permits limited axial movements of the disks 66 and 67. Theclutch disk 66 comprises a ring-shaped inner portion or nave 69 and aconcentric outer ring-shaped portion or rim 70. The ring-shaped portions69, 70 are connected to each other by a plate-like plastic annulus 68.The braking disk 67 is provided with an annulus of axially parallelelongated holes or slots 71 which are located between a ring-shapedinner portion or nave 72 and an outer ring-shaped portion or rim 73which is magnetically insulated from the inner portion 72, at least to asubstantial degree. The disks 66,67 are located between the flywheel 56and a stationary braking member 74. Those end faces of the ring-shapedportions 69, 70 and 72, 73 which respectively face the flywheel 56 andthe braking member 74 constitute pole faces and are provided withannular recesses for ring-shaped friction generating facings 75, 76. Theexposed surfaces of the facings 7 5, 76 are flush with the respectivepole faces. The ring-shaped portions 69, 70 and 72, 73 preferablyconsist of sintered. iron which is permeated with a synthetic plasticlubricant, such as polytetrafluoroethylene. The facings 75, 76preferably consist of sintered bronze which is also permeated withpolytetrafluoroethylene.

The disks 66, 67 are further provided with axially parallel coolingchannels 77, 78 which communicate with the channels 60 of the flywheel56 and with radi' ally extending cooling channels 79 which are providedbetween the braking member 74 and a plate 80. The braking member 74 isscrewed or bolted to the bearing member 62 and the plate 80 is alsoscrewed or bolted to the bearing member 62 and supports the medianantifriction bearing 64 for the driven shaft 12. the bearing member 62is formed with annuli of preferably equidistant air-admitting inletopenings 81 and with axially spaced air-evacuating or outlet openings82.

The annular space between the disks 66, 67 accommodates a frame 83 forthe two ring-shaped windings 42, 43. The winding-supporting portion ofthe frame 83 has a substantially I-shaped cross-sectional outline andcomprises two halves which are at least nearly mirror symmetrical withreference to a plane which is normal to the common axis of the shafts l,12 and extends midway between the disks 66, 67. The frame 83 isconnectedwith the bearing member 62 by means of screws, bolts or analogousfasteners. The radially outermost portion or flange 84 of the frame 83is concentric with and surrounds the rims 70, 73 of the disks 66, 67with minimal clearance. It will be noted that portions of the rims 70,73 extend axially beyond the respective ends of the flange 84.

The operation of the structure shown in FIG. 2 is generally identicalwith the operation of the structure shown in FIG. 1. When the winding 42is energized, the disk 66 is caused to adhere to the flywheel 56 by amagnetic flux which is indicated by the broken line 85. This insuresthat the driven shaft 12 rotates at the exact speed of the output shaft1 because the disk 66 cannot rotate with reference to the sleeve 16which is rigid with the shaft 12. When the winding 43 is energized, thedisk 67 is attracted to the braking member 74 by a magnetic flux whichis indicated by the broken line 86. The shaft 12 is then arrestedbecause the braking member 74 is stationary in contrast to the brakingmember 25 of FIG. 1 which is assumed to rotate at a speed less than thespeed of the output shaft 1. The blades 58 of the continuously drivenflywheel 56 induce a cooling air stream 87 which enters the clutchhousing by way of the inlet openings 81 and passes through the radialchannels 79 behind the braking member 74, thereupon through the axiallyparallel channels 78, 77 of the disks 67, 66 and radial channels 60 ofthe flywheel 56 to be discharged by way of the outlet openings 82.

The mass of the disks 66, 67 can be reduced still further if the innerportions of the naves 69, 72 are made of light metal or a lightweightsynthetic plastic material. Thus, those portions of the disks 66, 67which are splined to transmit torque or braking force to the plasticsleeve 16 on the driven shaft 12 can be made of a material whosespecific weight is substantially less than the specific weight ofremaining outer parts of the disks. The channels 77, 78 can be providedin the just mentioned plastic portions of the disks 66, 67. Such plasticportions are pressfltted into or otherwise securely affixed to themagnetically conductive outer portions of the respective disks.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention thatothers can,

by applying current knowledge, readily adapt it for various applicationswithout omitting features which fairly constitute essentialcharacteristics of the generic and specific aspects of my contributionto the art, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended 1. A structure of the character indicated,comprising coaxial driving and driven shafts; a flywheel secured to saiddriving shaft; a braking member axially spaced from said flywheel; firstand second disks disposed intermediate said flywheel and said brakingmember and axially movable secured to and rotatable with said drivenshaft, each of said disks comprising magnetically conductive concentricinner and outer ring-shaped portions, means for magnetically insulatingsaid ringshaped portions from each other and a friction generatingfacing between said inner and outer portions, the facing of said firstdisk being adjacent to said flywheel and the facing of said second diskbeing adjacent to said braking member, the facings of said first andsecond disks respectively comprising exposed surfaces adjacent to saidflywheel and said braking member and said inner and outer portions ofsaid disks having pole faces which are flush with the exposed surfacesof the respective facings, said facings and said inner and outerportions of said disks consisting of materials having at leastsubstantially identical resistance to wear; and a pair of windingsenergizable to respectively urge the facings of said first and seconddisks against said flywheel and said braking member.

2. A structure as defined in claim 1, wherein said windings are annularwindings which are coaxial with said shafts and further comprisingstationary frame means mounting said windings between said disks.

3. A structure as defined in claim 1, wherein said facings arering-shaped.

4. A structure as defined in claim 1, wherein said disks define anannular space the radially innermost portion of which is flanked by theinner portions of said disks and further comprising stationary framemeans extending into said space and supporting said windings.

5. A structure as defined in claim 4, wherein said frame means comprisesa ring-shaped portion of lshaped profile and including inner and outerflange means which are respectively adjacent to said inner and outerportions of said disks.

6. A structure as defined in claim 5, wherein said inner flange meanssurrounds said inner portions of said disks and said other flange meansis surrounded by said outer portions of said disks.

7. A structure as defined in claim 1, wherein said pole faces of saidinner and outer portions of said first and second disks respectivelyengage said flywheel and said braking member in response to energizationof the respective windings.

8. A structure as defined in claim 1, wherein said flywheel, saidbraking member and said disks are provided with communicating channelsand said flywheel comprises means for inducing the flow of at least onestream of cooling air through said channels in response to rotation ofsaid driving shaft.

9. A structure as defined in claim 1, further comprising blade meansprovided on said flywheel for inducing the flow of at least one streamof cooling air through axially parallel channels provided in the innerportions of said disks in response to rotation of said driving shaft.

10. A structure as defined in claim 1, further comprising blade meansprovided on said flywheel to induce the flow of at least one cooling airstream along the outer portions of said disks in response to rotation ofsaid driving shaft.

11. A structure as-defined-in claim 1, wherein said facings arerespectively separated from said flywheel and said braking member by airgaps of predetermined width in deenergized condition of the respectivewindings, and further comprising adjusting means for varying the widthof said air gaps.

12. A structure as defined in claim 1, wherein said means formagnetically insulating comprises plate-like annuli disposed between thethe inner and outer ringshaped portions of the respective disks, saidfacings being attached to the respective plate-like annuli.

13. A structure as defined in claim 12, wherein said plate-like annuliconsist of light metal.

14. A structure as defined in claim 12, wherein said plate-like annuliconsist of synthetic plastic material.

15. A structure of the character indicated, comprising coaxial drivingand driven shafts; a flywheel secured to said driving shaft; a brakingmember axially spaced from said flywheel; first and second disksdisposed intermediate said flywheel and said braking member and axiallymovably secured to and rotatable with said driven shaft, each of saiddisks comprising magnetically conductive concentric inner and outerring-shaped portions, means for magnetically insulating said ringshapedportions from each other and a friction generating facing between saidinner and outer portions, the facing of said first disk being adjacentto said flywheel and the facing of said second disk being adjacent tosaid braking member; and a pair of windings energizable to respectivelyurge the facings of said first and second disks against said flywheeland said braking member, said inner and outer portions of said first andsecond disks comprising pole faces which respectively engage saidflywheel and said braking member in response to energization of therespective windings, at least those parts of said inner and outerportions of at least one of said disks which are adjacent to therespective pole faces consisting of magnetically conductive sinteredmetal which is impregnated with a synthetic plastic lubricant.

16. A structure as defined in claim 15, wherein said metal is iron andsaid lubricant is polytetrafluoroethylene.

17. A structure of the character indicated, comprising coaxial drivingand driven shafts; a flywheel secured to said driving shaft; a brakingmember axially spaced from said flywheel; first and second disksdisposed intermediate said flywheel and said braking member and axiallymovably secured to and rotatable with said driven shaft, each of saiddisks comprising magnetically conductive concentric inner and outerring-shaped portions, means for magnetically insulating said ringshapedportions from each other and a friction generating facing between saidinner and outer portions, each of said facings consisting of amagnetically nonconductive sintered metal which is impregnated with asynthetic plastic lubricant, the facing of said first disk beingadjacent to said flywheel and the facing of said second disk beingadjacent to said braking member;

and a pair of windings energizable to respectively urge the facings ofsaid first and second disks against said flywheel and said brakingmember.

18. A structure as defined in claim 17, wherein said metal is bronze andsaid lubricant is polytetrafluoroethylene.

19. A structure of the character indicated, comprising a housing;coaxial driving and driven shafts; a flywheel located in said housingand secured to said driving shaft; a braking member located in saidhousing and axially spaced from said flywheel, said housing comprising afirst annular portion supporting said flywheel and said driving shaftand a second annular portion supporting said driven shaft; first andsecond disks in said housing, said disks being disposed intermediatesaid flywheel and said braking member and being axially movably securedtoand rotatable with said driven shaft, each of said disks comprisingmagnetically conductive concentric inner and outer ring-shaped portions,means for magnetically insulating said ring.- shaped portions from eachother and a friction generating facing between said inner and outerportions, the facing of said first disk being adjacent to said flywheeland the facing of said second disk being adjacent to said brakingmember; a pair of windings energizable to respectively urge the facingsof said first and second disks against said flywheel and said brakingmember, said facings being respectively separated from said flywheel andsaid braking member by air gaps of predetermined width in deenergizedcondition of the respective windings; and adjusting means for varyingthe width of said air gaps, said adjusting means comprising at least oneinsert removably interposed between said first and second annularportions of said housing.

20. A structure of the character indicated, comprising a housing;coaxial driving and driven shafts; a flywheel located in said housingand secured to said drive shaft; a braking member located in saidhousing and axially spaced from said flywheel; first and second disks insaid housing, said disks being disposed intermediate said flywheel andsaid braking member and being axially movably secured to and rotatablewith said driven shaft, each of said disks comprising magneticallyconductive concentric inner and outer ring-shaped portions, means formagnetically insulating said ringshaped portions from each other and afriction generating facing between said inner and outer portions, thefacing of said first disk being adjacent to said flywheel and the facingof said second disk being adjacent to said braking member, said housingcomprising a first annular portion supporting said braking member and asecond annular portion supporting said second disk; a pair of windingsenergizable to respectively urge the facings of said first and seconddisks against said flywheel and said braking member, said facings beingrespectively separated from said flywheel and said braking member by airgaps of predetermined width in deenergized condition of the respectivewindings; and adjusting means for varying the width of said air gaps,said adjusting means comprising at least one insert removably receivedbetween said annular portions of said housing.

21. A structure of the character indicated, comprising coaxial drivingand driven shafts; a flywheel secured to said driving shaft; a brakingmember axially spaced from said flywheel; first and second disksdisposed intermediate said flywheel and said braking member and axiallymovably secured to and rotatable with said driven shaft, each of saiddisks comprising magnetically conductive concentric axially extendinginner and outer ring-shaped portions and said inner portions of saiddisks being provided with channels, means for magnetically insulatingsaid ring-shaped portions from each other and a friction generatingfacing between said inner and outer portions, the facing of said firstdisk being adjacent to said flywheel and the facing of said second diskbeing adjacent to said braking memher; a pair of windings energizable torespectively urge the facings of said first and second disks againstsaid flywheel and said braking member; and means includand second sidesof said flywheel.

1. A structure of the character indicated, comprising coaxial drivingand driven shafts; a flywheel secured to said driving shaft; a brakingmember axially spaced from said flywheel; first and second disksdisposed intermediate said flywheel and said braking member and axiallymovable secured to and rotatable with said driven shaft, each of saiddisks comprising magnetically conductive concentric inner and outerring-shaped portions, means for magnetically insulating said ring-shapedportions from each other and a friction generating facing between saidinner and outer portions, the facing of said first disk being adjacentto said flywheel and the facing of said second disk being adjacent tosaid braking member, the facings of said first and second disksrespectively comprising exposed surfaces adjacent to said flywheel andsaid braking member and said inner and outer portions of said diskshaving pole faces which are flush with the exposed surfaces of therespective facings, said facings and said inner and outer portions ofsaid disks consisting of materials having at least substantiallyidentical resistance to wear; and a pair of windings energizable torespectively urge the facings of said first and second disks againstsaid flywheel and said braking member.
 2. A structure as defined inclaim 1, wherein said windings are annular windings which are coaxialwith said shafts and further comprising stationary frame means mountingsaid windings between said disks.
 3. A structure as defined in claim 1,wherein said facings are ring-shaped.
 4. A structure as defined in claim1, wherein said disks define an annular space the radially innermostportion of which is flanked by the inner portions of said disks andfurther comprising stationary frame means extending into said space andsupporting said windings.
 5. A structure as defined in claim 4, whereinsaid frame means comprises a ring-shaped portion of I-shaped profile andincluding inner and outer flange means which are respectively adjacentto said inner and outer portions of said disks.
 6. A structure asdefined in claim 5, wherein said inner flange means surrounds said innerportions of said disks and said other flange means is surrounded by saidouter portions of said disks.
 7. A structure as defined in claim 1,wherein said pole faces of said inner and outer portions of said firstand second disks respectively engage said flywheel and said brakingmember in response to energization of the respective windings.
 8. AstruCture as defined in claim 1, wherein said flywheel, said brakingmember and said disks are provided with communicating channels and saidflywheel comprises means for inducing the flow of at least one stream ofcooling air through said channels in response to rotation of saiddriving shaft.
 9. A structure as defined in claim 1, further comprisingblade means provided on said flywheel for inducing the flow of at leastone stream of cooling air through axially parallel channels provided inthe inner portions of said disks in response to rotation of said drivingshaft.
 10. A structure as defined in claim 1, further comprising blademeans provided on said flywheel to induce the flow of at least onecooling air stream along the outer portions of said disks in response torotation of said driving shaft.
 11. A structure as defined in claim 1,wherein said facings are respectively separated from said flywheel andsaid braking member by air gaps of predetermined width in deenergizedcondition of the respective windings, and further comprising adjustingmeans for varying the width of said air gaps.
 12. A structure as definedin claim 1, wherein said means for magnetically insulating comprisesplate-like annuli disposed between the the inner and outer ring-shapedportions of the respective disks, said facings being attached to therespective plate-like annuli.
 13. A structure as defined in claim 12,wherein said plate-like annuli consist of light metal.
 14. A structureas defined in claim 12, wherein said plate-like annuli consist ofsynthetic plastic material.
 15. A structure of the character indicated,comprising coaxial driving and driven shafts; a flywheel secured to saiddriving shaft; a braking member axially spaced from said flywheel; firstand second disks disposed intermediate said flywheel and said brakingmember and axially movably secured to and rotatable with said drivenshaft, each of said disks comprising magnetically conductive concentricinner and outer ring-shaped portions, means for magnetically insulatingsaid ring-shaped portions from each other and a friction generatingfacing between said inner and outer portions, the facing of said firstdisk being adjacent to said flywheel and the facing of said second diskbeing adjacent to said braking member; and a pair of windingsenergizable to respectively urge the facings of said first and seconddisks against said flywheel and said braking member, said inner andouter portions of said first and second disks comprising pole faceswhich respectively engage said flywheel and said braking member inresponse to energization of the respective windings, at least thoseparts of said inner and outer portions of at least one of said diskswhich are adjacent to the respective pole faces consisting ofmagnetically conductive sintered metal which is impregnated with asynthetic plastic lubricant.
 16. A structure as defined in claim 15,wherein said metal is iron and said lubricant ispolytetrafluoroethylene.
 17. A structure of the character indicated,comprising coaxial driving and driven shafts; a flywheel secured to saiddriving shaft; a braking member axially spaced from said flywheel; firstand second disks disposed intermediate said flywheel and said brakingmember and axially movably secured to and rotatable with said drivenshaft, each of said disks comprising magnetically conductive concentricinner and outer ring-shaped portions, means for magnetically insulatingsaid ring-shaped portions from each other and a friction generatingfacing between said inner and outer portions, each of said facingsconsisting of a magnetically nonconductive sintered metal which isimpregnated with a synthetic plastic lubricant, the facing of said firstdisk being adjacent to said flywheel and the facing of said second diskbeing adjacent to said braking member; and a pair of windingsenergizable to respectively urge the facings of said first and seconddisks against said flywheel and said braking member.
 18. A structure aSdefined in claim 17, wherein said metal is bronze and said lubricant ispolytetrafluoroethylene.
 19. A structure of the character indicated,comprising a housing; coaxial driving and driven shafts; a flywheellocated in said housing and secured to said driving shaft; a brakingmember located in said housing and axially spaced from said flywheel,said housing comprising a first annular portion supporting said flywheeland said driving shaft and a second annular portion supporting saiddriven shaft; first and second disks in said housing, said disks beingdisposed intermediate said flywheel and said braking member and beingaxially movably secured to and rotatable with said driven shaft, each ofsaid disks comprising magnetically conductive concentric inner and outerring-shaped portions, means for magnetically insulating said ring-shapedportions from each other and a friction generating facing between saidinner and outer portions, the facing of said first disk being adjacentto said flywheel and the facing of said second disk being adjacent tosaid braking member; a pair of windings energizable to respectively urgethe facings of said first and second disks against said flywheel andsaid braking member, said facings being respectively separated from saidflywheel and said braking member by air gaps of predetermined width indeenergized condition of the respective windings; and adjusting meansfor varying the width of said air gaps, said adjusting means comprisingat least one insert removably interposed between said first and secondannular portions of said housing.
 20. A structure of the characterindicated, comprising a housing; coaxial driving and driven shafts; aflywheel located in said housing and secured to said drive shaft; abraking member located in said housing and axially spaced from saidflywheel; first and second disks in said housing, said disks beingdisposed intermediate said flywheel and said braking member and beingaxially movably secured to and rotatable with said driven shaft, each ofsaid disks comprising magnetically conductive concentric inner and outerring-shaped portions, means for magnetically insulating said ring-shapedportions from each other and a friction generating facing between saidinner and outer portions, the facing of said first disk being adjacentto said flywheel and the facing of said second disk being adjacent tosaid braking member, said housing comprising a first annular portionsupporting said braking member and a second annular portion supportingsaid second disk; a pair of windings energizable to respectively urgethe facings of said first and second disks against said flywheel andsaid braking member, said facings being respectively separated from saidflywheel and said braking member by air gaps of predetermined width indeenergized condition of the respective windings; and adjusting meansfor varying the width of said air gaps, said adjusting means comprisingat least one insert removably received between said annular portions ofsaid housing.
 21. A structure of the character indicated, comprisingcoaxial driving and driven shafts; a flywheel secured to said drivingshaft; a braking member axially spaced from said flywheel; first andsecond disks disposed intermediate said flywheel and said braking memberand axially movably secured to and rotatable with said driven shaft,each of said disks comprising magnetically conductive concentric axiallyextending inner and outer ring-shaped portions and said inner portionsof said disks being provided with channels, means for magneticallyinsulating said ring-shaped portions from each other and a frictiongenerating facing between said inner and outer portions, the facing ofsaid first disk being adjacent to said flywheel and the facing of saidsecond disk being adjacent to said braking member; a pair of windingsenergizable to respectively urge the facings of said first and seconddisks against said flywheel and said braking member; and means includingfirst and second blade means pRovided on said flywheel and respectivelyarranged to induce the flow of at least one first cooling air streamaxially along said outer ring-shaped portions of said disks and at leastone second cooling air stream through said channels of said innerportions of said disks.
 22. A structure as defined in claim 21, whereinsaid flywheel has a first side facing said first disk and a second sideopposite said first side, said first and second blade means beingrespectively provided at said first and second sides of said flywheel.